Liverpool weirdness.

[Tantalus]

So, last night I fired up the Liverpool. Typically there's a noisy heater in the room where I play, but it wasn't terribly cold, so the heater and its whine were gone. Then the weirdness began. Power switch on. Transformer hum. Not a loud hum, but louder than it should be. I found that the hum is actually being transferred through the speakers with the standby switch off. It's still quiet, granted, but it's there. Standby on. Hum is amplified. Again, it's not overwhelming, but still noticeable. So out of sheer curiosity, I began voltage checks (Pacific transformers, tubes in, standby on.)

Mains: 117V
Sec.: 600v
B+1: 382
B+2: 372
B+3: 313
B+4: 297
B+5: 282

V4-V7

Plate: 380v
Screen: 369
Cathode: 36
Grid: ~0.015 (heavy fluctuation)

Concerning V1-V3, whenever I try and take any reading, there is a god-awful pop and feedback exploding through the speakers. Even with the volume knob completely off, it's painfully loud. I didn't attempt any further readings there.

Something I should mention. I found out very recently the house I'm in isn't properly grounded. It was built in the 1920's, and while there are grounded plugs in certain rooms of the house, the house itself isn't grounded. Could all of these issues be a consequence of that? I do pick up cellphone interference through the speakers at times, and some of the buzz dissipates when I touch the chassis. With the guitar plugged in, there is a horrendous buzz when I take my hands away from the strings or controls (very noticeable on the Telecaster.) So, quite obviously, all of this points to grounding problems. I was just curious if that could have an effect on operating voltages. That's what worries me right now. And for what it's worth, the amp sounds incredible. I'm not having any issues with it, outside of what I mentioned. No red-plating, etc. If anyone can offer advice, I'd be really grateful. Thanks.

[geetarpicker]

Typically, if when you take your hands off the strings the noise is much worse it is due to an open ground. So yes, you need to look into adding a ground or even perhaps a clip lead to a nearby cold water pipe might work if there is no PVC plastic pipe inline. That said, an open ground should have no effect on your voltages.

[Bob S]

You're house ground is a serious problem.
Like Glen says - a ground stake or connecting to the metal plumbing will help.
Which output tubes are you using ? 380 on the plates is high for new production tubes.
If your power transformer has dual secondaries, switch to the lower voltage.
For the feedback problem - disconnect the feedback wire to the presence pot
to see if it goes way. Make sure to insulate the disconnected wire.
The pop is normal when you probe with the amp powered up.
If you have probe clips, connect them with the amp off, then power on.
The best sounding Liverpools I've heard are right on the edge of stability.
So you're close.
Keep posting - almost there !

[Tantalus]

Thanks, Glen and Bob. I agree, the ground is a huge problem. This isn't my permanent residence, but I'll look into a grounding stake soon.

After reading through old posts last night, I ended up (you called it, Bob) switching secondaries on the PT. Here are the voltages now:

Sec.: 500V
B+1: 336v
B+2: 325
B+3: 273
B+4: 258
B+5: 246

V1

Pin 1: 188
3: 1.67
6: 169
8: 1.24

V2

1: 237
3: 2.43

V3

1. 222
2. 38
6. 222
7. 33
8. 53

V4-V7

Plate: 331
Screen: 325
Cathode: 25
Grid: 0.015

Pretty damned close, methinks. I've also switched over to 5k2 from 6k6 on the OT. I've not had a chance to play through it yet, but I'll report back.

[chuck]

I'm open to correction since I don't post here much, but it seems to me that 25V of bias is REALLY high for EL84's. What is the measured value of your cathode resistor?

Installing a ground isn't hard to do. You should first check to see if any of the grounded plugs in your place actually have the ground connected to anything. And if yes, what? Connecting grounded outlets in an otherwise ungrounded house and then connecting the ground pin terminal to a water pipe is old school electrician stuff and I think it used to pass code (in the states I lived in). Not sure about the specifics of that now (or in your location). It works just fine. But as Glen said, any PVC interruption in the pipe breaks the connection to ground. I'll guess that the grounded plugs in your house are in the kitchen and bathroom/s, is this right? If yes then it's likely they are actually grounded because that probably would have been a code upgrade. This assumes, again, that you're grounded through the plumbing and no PVC interruption in the metal piping has happened since. It should be checked.

As to having audible hum in the speaker with the standby "off" (amp not in play mode, which is actually standby ON), that's not right. If it is hum and not the buzz that is otherwise plaguing you then it's likely coupling 60Hz EM from the PT to the OT. No other way to get signal to the speakers with the HV off the OT. Are your transformers oriented correctly? If yes then you can try a trick that Ken Fischer use to do. Temporarily add some lead length to the OT leads and unbolt it. You need to be certain that no HV can touch any ground. Then, with the amp on, hold the OT (in a gloved hand) in position and just move it around until you find a nice quiet spot. Mount your OT there and trim the leads back as they should be.

Chuck

[Darkbluemurder]

Did you ground the speaker jack to the chassis?

Cheers Stephan